Late in the evening on Wednesday 9 October, 1957, scientists working at the Windscale atomic factory in Cumbria noticed something unusual. The temperature of the graphite blocks in one of the reactors, known as Pile 1, was rising steadily. This was slightly alarming.

The technicians were in the process of releasing a build-up of energy – a routine procedure – and the temperature in the core should have been falling.

In an effort to cool the reactor, more air was pumped in. But by midday the following day, temperatures were rising even quicker. To make matters worse, sensors at the top of Pile 1's giant cooling chimney were registering high levels of radioactivity.

When workers, clad in protective suits, removed an inspection plug at the front of the reactor, they saw, to their horror, that several fuel rods containing uranium had burst and their contents were on fire. This was now a full-scale emergency and one for which no one had planned and for which there was no operating procedure.

Hundreds more fuel rods were in danger of going up in flames and, already, a plume of radioactive iodine, caesium and polonium had escaped through the chimney and was making its way across north-west England.

In desperation, the team at the site rushed to the charge face – the 50ft 'wall' where fuel is loaded into the reactor – and attacked the rods with sledgehammers and bits of scaffolding in an effort to dislodge them.

In the end, it took two days to put the fire out. Catastrophe was avoided. But, contrary to the official statement, which claimed that the release of radiation was not hazardous and had been 'carried out to sea by the wind', the impact of the fire on human health was devastating.

Local farmers and villagers received a radiation dose 10 times higher than the maximum permitted in a lifetime, and over the years it is estimated that more than 250 people succumbed to cancers.

There was another casualty that night. People's confidence in nuclear technology was dented for the first time and the reputation of an industry that had promised clean and plentiful energy 'too cheap to meter', began its slow and steady decline.

Today, as you approach Windscale from the A595 on the western fringe of the Lake District National Park, Pile 1 still dominates the vista; the thickest of a series of towers looming over the Cumbrian countryside.

The site changed its name to Sellafield in 1981 as part of a re-branding exercise following the fire (and a succession of further incidents and accidents), but the crippled reactor still stands because no one has yet perfected a safe way to remove it.

Some of the nuclear material inside the core is thought to have a half-life of several thousand years – that is, it will take this amount of time for it to lose half its radioactivity – and is so dangerous that, if you stood next to it, you would receive a fatal dose of radiation within seconds.

Pile 1 and its sister reactor, Pile 2, were built with one purpose – to provide Britain with a nuclear bomb. But the site is also home to Britain's first civil nuclear power station, Calder Hall, which was opened by The Queen in 1956 and operated, on and off, until March 2003; and to another power station, opened in 1962 and shut in 1981.

The contents of these redundant buildings are also deadly, as are the dozens of facilities that handled their spent fuel and various by-products.

Cleaning them up, taking them apart and disposing of their radioactive material is an immensely time-consuming and complicated task, as Euan Hutton, Sellafield's head of decommissioning, explained to me when I toured the site on a grey, wet morning in September.

A barrel-chested Scot in his late thirties, who looks as if he came into the world wearing a hard-hat, Hutton has been working at Sellafield for 17 years and exudes an easy authority that comes from grappling with some of engineering's most fiendish puzzles.

'You've got to remember,' he remarked as we walked along a road at the heart of the four-square-mile site, 'that a lot of these buildings were built in a hurry back in the 1940s and 1950s. It was an incredible achievement to put these buildings up, but they didn't really think about how they were going to take them apart when they were finished.

'They didn't even keep accurate drawings of what they did, because there were scientists over there' – he gestured to a low-level brick building – 'with test-tube-size science saying, ''Yeah, that works, put a big one of those in there please.'' So when we come along it's not like we can just take out the book and say, ''What did they do where?"'

Instead, Hutton and his team track down people who used to work at Windscale, take them out for lunch and see what they can remember, to acquire as much 'characterisation' of the buildings as they can. Then they have to work out how to take them apart – another long process – before they are in a position to start up a grinder.

It also takes years, and tens of millions of pounds, to design the robots that are needed to handle the most radioactive material. And every step of the way, Sellafield has to prove to the industry's regulators that it is meeting safety standards, a process that takes yet more time.

In September 2007, a landmark was reached – or, more accurately, demolished – when explosive experts took down the four giant Calder Hall cooling towers, in front of a crowd of 20,000 standing in the surrounding fields.

A £500 million plan is also in place, at last, to start extracting the damaged fuel rods from the core of Pile 1, with a view to finally demolishing the building in 2020.

But the clean-up of the rest of Sellafield (which accounts for 70 per cent of Britain's so-called 'legacy waste' in terms of volume, and 90 per cent in terms of radioactivity) is expected to last another 112 years – at a cost to the taxpayer of £33.5 billion.

To decommission Britain's 10 other active nuclear plants, when they come to the end of their useful lives, is expected to cost £40 billion on top of that.

With such huge bills and the generation of so much poisonous material it seems astonishing that the nuclear industry was allowed to power even one single light bulb. But hindsight is always an exact science.

During the 1960s and 1970s neither of these drawbacks was fully realised by either politicians or the public. To the contrary, President Eisenhower had inspired many with his speech about 'Atoms for Peace', which encouraged the world's nuclear powers to beat swords into ploughshares and focus on peaceful uses for atomic energy.

Harold Macmillan had suppressed the full report into the Windscale fire (the facts weren't made public for 30 years) and even the dyed-in-the-wool socialist Tony Benn supported the expansion of civil nuclear power when he was appointed Minister of Technology in 1966, trumpeting it as 'cheap, safe and peaceful'.

Only as the Cold War ground on, and the hideous consequences of nuclear fall-out rooted themselves in the public consciousness, did an anti-nuclear sentiment begin to grow in this country. Newspapers reported blunders at various power stations and then, in 1979, a partial meltdown occurred at the Three Mile Island nuclear plant in Pennsylvania.

No one was killed in that accident and the amount of radiation released into the atmosphere had a negligible effect on human health, but the psychological impact was profound. Support for nuclear power among the general public in America fell from 70 per cent to 50 per cent.

In 1986, that support, both in America and Britain, tumbled even further when Chernobyl exploded. This time the effects of radiation were felt all the way from the Ukraine to the hills of Snowdonia, where sheep farmers to this day face Geiger-counter checks on the level of radioactivity in their flocks.

Yet it was neither Chernobyl, nor anti-nuclear protesters, that condemned the industry to years in the political wilderness. It was Margaret Thatcher.

When her Government moved to privatise the nation's nuclear plants in the late 1980s, the City took one look at the accounts and ran a mile. Billions of pounds, it transpired, had been wasted on impractical, uncommercial reactor designs, and billions more were required to deal with spent fuel, nuclear waste and decommissioning.

At a time when oil prices were relatively low and Britain was benefiting from cheap North Sea gas, it was hard to make a case for nuclear power, and of the 10 new plants that the Government had said it wanted to build, only one – Sizewell B in Suffolk – ever went ahead.

British Energy, which runs eight of the country's nuclear sites, was part-privatised in 1996, but the industry remained in the doldrums. In 1997, Labour's manifesto didn't mince its words. 'We see no economic case,' it said, 'for the building of any new nuclear power stations.'

Since then, a series of cock-ups and cover-ups has done nothing to dispel the industry's reputation for profligacy, secrecy and complacency.

In 2000, a report by the Health and Safety Executive's Nuclear Installations Inspectorate startled even seasoned anti-nuclear campaigners when it revealed that workers at Sellafield had been faking quality-assurance data for four years – copying old records rather than carrying out new tests. The scandal led to the resignation of John Taylor, the chief executive of British Nuclear Fuels, which ran the Cumbrian site.

Separate investigations since then have been hardly less alarming, finding, among other things, safety measures based on 'guesswork'; alarm bells routinely ignored; safety equipment left broken; cracks in crucibles containing highly radioactive nuclear waste; 'intermediate' waste on the verge of exploding; and major cracks in the graphite bricks used to make the reactors in some of Britain's older power stations.

In March 2004, declassified RAF documents obtained by the Labour MP Llew Smith showed there had been 49 cases since 2000 of 'near-misses' by fighter jets flying too close to nuclear stations. Most worrying of all, in May 2005, it was revealed that 83,000 litres of radioactive waste – enough to fill half an Olympic swimming pool – had leaked from a cracked pipe at Sellafield. It was the worst nuclear accident for 13 years.

The leak took place in Thorp – the Thermal Oxide Reprocessing Plant – where Sellafield takes spent nuclear fuel from reactors worldwide and separates it into uranium and plutonium. Not only had the plant not owned up to the leak (it was the subject of an inspection report uncovered by a newspaper) but the pipe had first cracked in August 2004 and the leak had gone unnoticed for up to nine months.

So, it's not altogether surprising that the Government, until recently, seemed happy to allow Britain's nuclear stations to burn themselves out and planned to fill the gap – nuclear provides a little under a fifth of the country's electricity – with more coal, oil and gas plants. Today, that policy sounds like something from another age. The industrialised world has become obsessed by the perils of global warming; and fossil fuels, which spew millions of tonnes of carbon into the atmosphere, are deeply unfashionable.

They are also expensive. Oil reached almost $150 a barrel earlier this year, and gas, the price of which rose side-by-side with oil, is set to become even more costly as our supplies in the North Sea dry up and we rely increasingly on unstable regions such as Russia, the Middle East and Africa.

Nuclear plants, which emit hardly any CO2 once they're built and whose raw material, uranium, comes from friendly countries such as Canada and Australia, are suddenly back in vogue. In a speech in July this year, Gordon Brown made it clear: with all but one of the country's nuclear plants due to shut down by 2023, Britain must act now to ensure they were replaced.

Calling for a 'renaissance of nuclear power', as well as investment in 'renewables' such as wind farms, he said: 'The years of cheap energy and careless pollution are behind us. We need a new strategy. Past total dependence on oil must give way to a clean energy future.'

To get an idea of what that future might look like, you could do worse than visit Sizewell B on the Suffolk coast. Opened in 1995, the station is the most efficient nuclear plant in Britain and appears pristine compared to the sprawling mess of Sellafield. Where the Cumbrian site is overflowing with ancient silos, skips, cranes, concrete blocks and Portakabins, Sizewell keeps its moving parts neatly parcelled away inside giant steel-clad buildings.

Outside, the wide tarmac is almost deserted. When I stand next to the massive turbine hall with Colin Tucker, one of the plant's safety engineers, and gaze up at the white dome of the reactor building behind it which blocks out the sun, it reminds me, bizarrely, of a Sunday morning among the empty streets of Wall Street, in Manhattan.

'Most of the equipment is in buildings and then inside concrete blocks inside those buildings,' says Tucker. 'That's why there aren't many people around.' And it is inside, of course, where the real sound-and-light show takes place.

Sizewell B is what is known as a Pressurised Water Reactor (PWR). It is the only one of its kind in Britain but EDF, the firm that is set to take over the plant from British Energy later this year, operates 58 similar stations in France and wants to build four more up-dated versions in Britain, one of which will probably be located next to Sizewell B and called, unsurprisingly, Sizewell C.

In essence, a PWR is based on a source of heat – the reactor – three circuits of water and two turbine generators that generate electricity. Inside the reactor is a series of tall, thin tubes known as fuel rods, and inside them is enriched uranium. If you hit enriched uranium with a slow-moving neutron it splits – or 'fissions' – and in doing that releases a tremendous amount of energy: about two million times more than that produced from burning a carbon atom.

As well as releasing energy, uranium releases other neutrons which can be slowed down and go on to make more fissions. That produces a chain reaction and that, in the case of Sizewell B, generates 3,500 megawatts of heat – the same amount as a million electric kettles.

This heats up water – 20 tonnes are pumped through the core every second – and this water then travels to boilers. On the other side of the boilers is a secondary circuit of water. The heat is transferred and the water turns into steam.

Sizewell makes two tonnes of steam per second and that steam is then piped into a series of giant fan blades known as turbines. The force of the steam causes the blades to spin at almost twice the speed of sound and this, in turn, generates 23,000 volts of electricity.

This goes to a transformer that boosts it to 400,000 volts and then, finally, electric cables take the electricity from the transformer out to the National Grid. Together, the two turbines generate 1,260 megawatts, enough electricity for two million homes or 3 per cent of the UK's entire electricity needs.

It is exhilarating, standing in the Turbine Hall, witnessing the creation of this power. Like all great engineering projects, it reminds you of mankind's extraordinary ingenuity. And it is reliable.

From 21 October 2006, the time of its eighth stoppage for refuelling, Sizewell B operated continuously for 516 days, and apart from the first week and the last two weeks, all of that period was at full power. The run before that was a continuous cycle of 471 days.

To produce the same output over a similar time-period, a coal station would have to burn about four million tonnes of coal, which would produce 500lb of carbon dioxide per second.

Of course, Sizewell still produces highly radioactive waste. Its spent fuel – fuel that has been irradiated until it is no longer useful in sustaining a nuclear reaction – contains radio-isotopes that will remain fatal to humans for thousands of years.

Other 'intermediate' waste, such as chemical filters and resins, and low-level waste, such as building rubble, is less toxic but still needs to be disposed of. And Sizewell B will still have to be decommissioned, at great cost, when it reaches the end of its life in 2035.

But on all these counts, Sizewell represents a substantial improvement on what has gone before. It generates a smaller volume of spent fuel than older Magnox and Advanced Gas-cooled Reactors (although it is three times more radioactive) and the used fuel it does produce is relatively easy to handle.

Other stations send their fuel rods to Sellafield for reprocessing, but at Sizewell they are taken out of the reactor and placed directly into a storage pond, which contains purified water, a natural barrier to radioactivity.

Here it will stay until a national repository – probably a concrete-filled cavern deep under-ground – is built sometime later this century.

Sizewell will also be far easier to decommission than older stations. In contrast to the 100-year clean-up required at Sellafield, British Energy expects to decommission the Suffolk plant within 10 years – something the firm says it knows is possible, because it has already been done at a power station in America (the only thing left on the site of the Connecticut Yankee plant is a dry-cask fuel store).

It is so much easier at these plants because the active parts, the bits you have to take apart carefully to avoid the radiation dose, are tiny compared with older stations and made from materials that are easier to clean-up.

Of course, not everyone is enamoured of Sizewell. Greenpeace is against nuclear power in all its forms and believes the money could be better spent on wind, wave and solar energy, none of which presents any risk to human health or the environment. The group also argues that the expansion of the civil nuclear industry increases the chances of a regime such as Iran, or a terrorist organisation such as al-Qa'eda, developing nuclear weapons.

'The sort of plants that EDF wants to build in the UK will use plutonium to make their fuel,' says Nathan Argent, who heads the Greenpeace nuclear campaign. 'And the company is already in advanced negotiations to sell the same technology – 90 per cent of which can be used for both civil and military purposes – to the United Arab Emirates, South Africa, India, China and Brazil. Spreading the technology like this increases the risk of [proliferation controls] being broken.'

Argent, a fast-talking environmental scientist who, before joining Greenpeace, was involved in a campaign against the illegal wildlife trade, is also sceptical about the Government's plan to build a geological repository for high-level waste.

His objections – that it's been devised on the back of an envelope' and is full of conjecture – are slightly overwrought, but it's true that the science has some way to go. The experts are just hoping these will be solved once a location has been chosen and the JCBs move in.

And, in common with all anti-nuclear campaigners, Argent is suspicious of an industry that has a long history of secrecy and cover-ups. Engineers such as Colin Tucker may say Sizewell is 'extremely stable', but that's what they said about Three Mile Island, in Pennsylvania, also a Pressurised Water Reactor, before it exploded in 1979.

When I ask Tucker, a member of Sizewell B's Nuclear Safety Group, about the possibility of an accident at the plant, the question brings him up short and, for the first time, he is almost lost for words. 'Er… I'm just trying to think of the best way to answer that…' he begins, exhaling loudly.

'If you're talking about credibility, there are a range of faults that can lead to a radioactive release that in turn would have consequences. Um… I'm trying to think of some ways of explaining that. Er…'

It seems he genuinely didn't expect to be challenged on such an issue; not because he doesn't think about these things, but because, for him, the failings of Three Mile Island are ancient history and the safety of Sizewell B is beyond question.

'In all practical senses of the word that you're used to in everyday life, it's safe,' he says finally, regaining his composure. 'In my job, nuclear safety, it's never absolutely safe because we worry about things that are in a one-in-10-million years fault sequence. What we won't do is spend time on sequences that are in the once-in-1,000-million years category. That gets a bit too unlikely even for us.'

A number of lessons were learnt after Three Mile Island, Tucker tells me. For example, operators at the American station were not well trained; and those that were on duty when the accident occurred blindly followed what turned out to be a flawed procedure.

Sizewell B provides a lot more training and also ensures two different sets of procedures are in place. One is run by the reactor operator, and seeks to identify the fault, if one occurs. The other is run by the control room supervisor, and examines the symptoms. 'So if one guy makes a mistake,' says Tucker, 'another guy can stop him doing anything seriously wrong.'

A stocky man with a pale face and a trim beard, Tucker is not given to wild claims. Like many people in the engineering profession, not least those charged with minimising the risk of a nuclear explosion, he has a precise manner and takes care over everything he says.

But, to him, talk of Britain abandoning nuclear power in favour of, say, a massive expansion in wind farms, is preposterous. Standing on a walkway at the north-west corner of the site, the engineer gestures out to sea.

'They're putting up 140 wind turbines down the coast at Harwich,' he tells me. 'They're going to be 180 metres tall, two-and-a-half times higher than our reactor building, and they're bringing the cables ashore here to connect to the grid. Together those turbines will generate about 160 megawatts on average. So you'd need seven wind farms of that size to match the output of this one reactor.'

Then he points to an area of land one mile square covered in grass and conifers to our left. It is owned by British Energy and will probably be the site of Sizewell C. 'We could place a twin-reactor station there,' he says. 'If we did that we could generate 10 per cent of the country's electricity.'

Tucker is not an emotional man, but I suspect the prospect of this makes his heart sing. The same cannot be said for those who live near the plant.

Residents of Sizewell village – a collection of houses and holiday homes next to the beach – do not want another blot on the landscape and say the present road system could not support the extra traffic created by Sizewell C.

But a number of villagers I spoke to were more concerned about the new wind farm, which they say will ruin the skyline.

'It's a fabulous place to live if you can block out Sizewell,' said Pat Hogan, a teacher. 'But I personally, and lots of people I speak to, do not want windmills, either in their view here or when they go to Scotland or wherever.'

Indeed, most residents in the village have come to terms with the nuclear issue. 'If you want heat and light and energy, somewhere along the line you have to put up with something,' said Ms Hogan.

It is a pragmatic attitude – and one other opponents might do well to emulate. Because if Sizewell C, and other new plants, are not built – if nuclear power is buried, along with its burning hot waste – all of us face a future that will be cold, difficult and dark.